Implantable neurostimulation systems have proven therapeutic in a wide variety of diseases and disorders. Pacemakers and Implantable Cardiac Defibrillators (ICDs) have proven highly effective in the treatment of a number of cardiac conditions (e.g., arrhythmias). Spinal Cord Stimulation (SCS) systems have long been accepted as a therapeutic modality for the treatment of chronic pain syndromes, and the application of tissue stimulation has begun to expand to additional applications, such as angina pectoris and incontinence. Further, in recent investigations, Peripheral Nerve Stimulation (PNS) systems have demonstrated efficacy in the treatment of chronic pain syndromes and incontinence, and a number of additional applications are currently under investigation.
More pertinent to the present inventions described herein, Deep Brain Stimulation (DBS) has been applied therapeutically for well over a decade for the treatment of neurological disorders. DBS and other related procedures involving implantation of electrical stimulation leads within the brain of a patient are increasingly used to treat disorders, such as Parkinson's disease, dystonia, essential tremor, seizure disorders, obesity, depression, restoration of motor control, and other debilitating diseases via electrical stimulation of one or more target sites, including the ventrolateral thalamus, internal segment of globus pallidus, substantia nigra pars reticulate, subthalamic nucleus (STN), or external segment of globus pallidus. DBS has become a prominent treatment option for many disorders, because it is a safe, reversible alternative to lesioning. For example, DBS is the most frequently performed surgical disorder for the treatment of advanced Parkinson's Disease. There have been approximately 30,000 patients world-wide that have undergone DBS surgery. Consequently, there is a large population of patients who will benefit from advances in DBS treatment options. Further details discussing the treatment of diseases using DBS are disclosed in U.S. Pat. Nos. 6,845,267 and 6,950,707, which are expressly incorporated herein by reference.
During DBS procedures, at least one burr hole is cut through the patient's cranium as not to damage the brain tissue below, a large stereotactic targeting apparatus is mounted to the patient's cranium, and a cannula is scrupulously positioned towards the target site in the brain. Microelectrode recordings may typically be made to determine if a trajectory passes through the desired part of the brain, and if so, the stimulation lead (or leads), which carries an array of electrodes, is then introduced through the cannula, through the burr hole, and along that trajectory into the parenchyma of the brain, such that the electrodes located on the lead are strategically placed at a target site in the brain of the patient. Typically, an imaging device, such as a magnetic resonant imager (MRI) or a computed tomography (CT) imager may be used to confirm the lead position. Once the lead is properly positioned, the portion of the lead exiting the burr hole is subcutaneously routed underneath the patient's scalp to a neurostimulator implanted in the patient at a site remote from the burr hole (e.g., the patient's chest region). The neurostimulator generates electrical stimulation pulses in accordance with a set of stimulation parameters programmed into the neurostimulator.
Significantly, it is crucial that proper location and maintenance of the lead position be accomplished in order to continuously achieve efficacious therapy. In DBS applications, the target site (or sites) that is intended for electrical stimulation is about the size of a pea and is located deep within the patient's brain. Thus, lead displacements of less than a millimeter may have a deleterious effect on the patient's therapy. Because the stimulation region needs to be in the correct location to achieve optimal therapy and minimization of side-effects, stimulation leads typically carry many electrodes (e.g., four), so that at least one of the electrodes is near the target and allow programming of the electrodes to place the stimulation field in that region of interest. To this end, after the stimulation leads are implanted within the brain of a patient and confirmed to be in the correct position relative to the target region, a fitting procedure is typically performed to select one or more effective sets of stimulation parameters for the patient.
Typically, the stimulation parameters programmed into the neurostimulator can be adjusted by manipulating controls on an external control device to modify the electrical stimulation provided by the neurostimulator system to the patient. Thus, in accordance with the stimulation parameters programmed by the external control device, electrical pulses can be delivered from the neurostimulator to the stimulation electrode(s) to stimulate or activate a volume of tissue in accordance with a set of stimulation parameters and provide the desired efficacious therapy to the patient. The best stimulus parameter set will typically be one that delivers stimulation energy to the volume of tissue that must be stimulated in order to provide the therapeutic benefit (e.g., treatment of movement disorders), while minimizing the volume of non-target tissue that is stimulated, which may results in side-effects. A typical stimulation parameter set may include the electrodes that are acting as anodes or cathodes, as well as the amplitude, duration, and rate of the stimulation pulses.
The large number of electrodes available, combined with the ability to generate a variety of complex stimulation pulses, presents a huge selection of stimulation parameter sets to the clinician or patient. To facilitate such selection, the clinician generally programs the external control device, and if applicable the neurostimulator, through a computerized programming system. This programming system can be a self-contained hardware/software system, or can be defined predominantly by software running on a standard personal computer (PC). The PC or custom hardware may actively control the characteristics of the electrical stimulation generated by the neurostimulator to allow the optimum stimulation parameters to be determined based on patient feedback and to subsequently program the external control device with the optimum stimulation parameters.
Despite the fact that a computerized programming system can be used to more efficiently program a neurostimulator, physicians and clinicians must still go through an extensive trial-and-error process to determine the stimulation parameter set or sets to be programmed into the neurostimulator. To address this concern, it is helpful to predict and display the size and location of the volume of tissue influenced by the stimulation provided the electrodes given a certain set of stimulation parameters (including electrode combination, pulse amplitude, pulse duration, and pulse frequency). For example, U.S. Pat. No. 7,346,382 describes a technique whereby a finite element model (FEM) of a defined candidate electrode morphology (which includes size, shape, and arrangement of electrodes) and surrounding tissue is solved for the second difference of the potential (Δ2Ve), and then the volume of tissue likely to be affected (the “volume of activation” (VOA)) by various sets of stimulation parameters (pulse amplitude, pulse duration, and pulse frequency) is predicted.
While the VOA prediction technique described in U.S. Pat. No. 7,346,382 is advantageous, there are certain inherent disadvantages associated with modeling the stimulation leads. For example, a substantial amount of time and effort must be spent in developing FEM models for each new lead design, thereby presenting a bottleneck for lead development. For example, each FEM lead model must not only take into account the variability in electrode size and shape, but also the variability in electrode position due to, e.g., intra-lead electrode spacing, different lead configurations (e.g., a closely spaced side-by-side configuration, a closely spaced top-bottom configuration, a widely spaced top-bottom configuration, or a widely spaced side-by-side configuration), stagger of the leads, etc. Furthermore, because it is highly desirable that the implementation of the software package installed within each computerized programming system take into account all commercially available stimulation leads, computerized programming systems previously released into the field must be upgraded with new FEM lead models each time a new stimulation lead is designed.
There, thus, remains a need for an improved method and system for modeling stimulation leads.